The present invention relates to vehicle braking systems and more particularly, to pressure control solenoid based systems.
Technical drawbacks have generally inhibited the actual application of pressure control solenoid valves in vehicle braking systems. One drawback is the development of a dependable, cost-effective pressure control solenoid valve that provides predictable and repeatable control pressure as a function of an electrical input signal.
This drawback has been addressed in the development of the present braking system by a device claimed in related application, U.S. Ser. No. 08/402,216 filed Mar. 10, 1995 now U.S. Pat. No. 5,571,248, entitled Pressure Regulator, which is commonly assigned and specifically incorporated herein by reference.
Another drawback is that a typical pressure control solenoid valve generally has a valve structure that inherently leaks. A conventional method of reducing the leakage of the valve is to minimize clearances between the valve's moving member and housing. This requires tight tolerances and may require selected fitting of the moving member into each individual housing. The general conventional approach is effective in reducing leakage but does not totally eliminate it. This conventional approach also tends to be costly and temperature sensitive.
Another drawback of conventional pressure control solenoid valve's is that closely toleranced valve components tend to exhibit an inherently undesirable condition due to a phenomenon called limit cycling. With limit cycling in conventional hydraulic servo-type valves, a large increase in flow gain is exhibited as the device overcomes a positive overlap between the valve's moving member and housing.